1. Field of the Invention
The present invention relates generally to the encryption of data for delivery on demand, and more particularly to an encryption device, a decryption device, a data delivery device, a data receiving device, a data delivery system, and media storing encryption and decryption programs applicable to, for example, the distribution of video content.
2. Description of the Related Art
In recent years, services that deliver movies and other video content on demand over the Internet have become popular. Video content is generally protected by copyright or other legal measures, so the content is encrypted to avoid unauthorized redistribution and viewing.
Video content delivered over the Internet may be pre-encrypted as disclosed in Japanese Patent Application Publication No. 2007-13765, or encrypted in real time during delivery.
With pre-encryption, there is no encryption processing load during delivery, but security is weaker than with real-time encryption, because if the encryption code is broken, the content remains vulnerable until the break is discovered and the content is re-encrypted with different encryption conditions. Another problem with pre-encryption is the need to store decryption keys.
Real-time encryption imposes a heavy encryption processing load during delivery, but the encryption keys or other encryption conditions are updated at every delivery, so even if the code is broken, security is not seriously compromised, and key management is easier because the decryption keys do not have to be stored. There is, however, a greater risk of unauthorized viewing or theft of video content by an insider who can gain access to the unencrypted content.
Systems that store the content in pre-encrypted form and then decrypt and re-encrypt the content on delivery have been developed, but these systems have a very high delivery processing load.
There is a need for an encryption device, a decryption device, a data delivery device, a data receiving device, a data delivery system, and media storing encryption and decryption programs that can prevent unauthorized use of data with a reduced delivery processing load.